Mining and tunneling apparatus involving alternated application of thermal and mechanical energy in response to sensed rock condition

ABSTRACT

A mining or tunneling apparatus is provided for continuous underground excavation through rock of relatively high to relatively low hardness. The apparatus comprises impactors and heaters having alternately operative and inoperative modes which are selected in reference to the sensed and indicated homogeneity of the rock condition of the excavation face. Functional relationships between the applied thermal and mechanical energy are given. Optional separation of ore and gangue at the mining face is outlined.

United States Patent Boyd et al.

MINING AND TUNNELING APPARATUS INVOLVING ALTERNATED APPLICATION OFTHERMAL AND MECHANICAL ENERGY IN RESPONSE TO SENSED ROCK CONDITIONInventors: James Boyd, 630 Fifth Ave. New

York, N.Y. 10020; Lawrence A. Garfield, 1505 Tary Ct. Colorado Springs,Colo. 08908; Clifford Hanninen, 14 Elm St. {P.O. Box 832). White Pine,Wis. 49971; Eugene Maki, White Pine Copper Company, White Pine, Mich.49971 Filed: Dec. 17, 1973 Appl. No: 425,263

Related U.S. Application Data Continuation of Ser. No. 332.552. Feb. 15,1973, abandoned.

U.S. Cl 299/l; 299/14 Int. Cl. EZIc 37/16 Field of Search .1 299/1, 14;239/4, 102

Apr. 8, 1975 [56] References Cited UNITED STATES PATENTS 1.28439811/1918 McKinlay ttttttttttttttttttttt 299/14 X 3.015.477 H1962 Perssonet al 299/1 3.700.169 10/1972 Nayden et al 239/102 X PrimaryE.\'aminerErnest R. Purser Attorney, Agent. or FirmMorse. Altman. Oates&

Belle 1 1 ABSTRACT A mining or tunneling apparatus is provided forcontinuous underground excavation through rock of relatively high torelatively low hardness. The apparatus comprises impactors and heatershaving alternately operative and inoperative modes which are selected inreference to the sensed and indicated homogeneity of the rock conditionof the excavation face. Functional relationships between the appliedthermal and mechanical energy are given. Optional separation of ore andgangue at the mining face is outlined.

6 Claims, l3 Drawing Figures PLIENIEBAPR 81975 (3.876.251

SHEET 1 OF 4 FIG.8

PATENTED 81975 3.876.251

sum 2 OF 4 FIG. IB

INCHES l l l l 3 6 9 l2 PATENTEDAPR 81975 sum u BF 4 FIG.5

FlG.4

FIG.7

m h H M S D N A s R E m VALUES-ONLY MINING FIG. 9

MINING AND TUNNELING APPARATUS INVOLVING ALTERNATEI) APPLICATION OFTHERMAL AND MECHANICAL ENERGY IN RESPONSE TO SENSEI) ROCK CONDITION Thisis a continuation. of application Ser. No. 332.552. filed Feb. 15. I973and now abandoned.

BACKGROUND The present invention relates to underground excavation and.more particularly. to excavation in rock for the purposes of mining andtunneling. Various prior excavation techniques have included: drillingand blasting; mechanical cutting; and thermal spalling. In the case ofthe drilling and blasting. holes are drilled mechanically into the rockface. are filled with an explosive charge such as dynamite. and theregion in the vicinity ofthe holes is fragmented by the explosive powerof the charge. In the case of the mechanical cutting. pneumatically.hydraulically or electrically actuated percussion moils or rotarycutting tools are applied to the excavation face. by which fragmentationof the rock at the face is effected. In the case of thermal spalling.heat from an intense source is transferred to the rock face in such away as to cause differential expansion of the region underlying the faceand to cause ten sile and/or shear strain separation of portions of therock therefrom. Drilling and blasting, relatively inefficient from thestandpoint of conversion of energy into loose rock and inadequatelycontrollable in the amounts and sizes of loose rock produced, inherentlyis a tortuous and interrupted process that concomitantly may requirecostly and time consuming installation of supports in portions of theexcavation region. which may be weakened by shock at considerabledistances from the excavation face. Mechanical cutting. although capableof more or less uninterrupted prodedures. has been found to beundesirably slow. particularly at deep levels. because of the strengthlimitations inherent in steel percussion and cutting tools. no matterhow sturdily designed. And thermal spalling has been used onlyoccasionally because ofthe large amounts of thermal energy needed. thelow efficiency of heat transfer generally achievable and the hazards andcost involved in removing the products when combustion heating is used.At present. excavation through rock having a Compressive strength of25,000 psi. (pounds per square inch) can be achieved at a rate ofapproximately to feet per day. In view of the increasing modern need forrapid excavation in hard rock. existing excavation rates have becomeinadequate.

SUMMARY OF THE INVENTION The primary object of the present invention isto provide an apparatus and process for continuous undergroundexcavation through rock of relatively high to relatively low hardness inrelation to a reference hardness that is relevant to the operation ofthe apparatus. The term hardness herein refers to rock condition insitu. The apparatus comprises an impacting assembly and a heatingassembly having alternately operative and inoperative modes. which areselected on the basis of the detected hardness of any excavation face.The impacting assembly has an operative mode. in which it ripssuccessively exposed excavation faces, and an inoperative mode. which isselected when the impacting assembly reaches an excavation face ofahardness that would subject elements of the impacting assembly to LIILII

uneconomic wear if the operative mode were to continue uninterruptedly.The heating assembly has an operative mode. in which it forms a kerf inany excavation face of relatively high hardness. and an inoperative modein which the impacting assembly can resume its ripping function withacceptable wear as a result of the presence of the kerf. It has beenfound that applying the heating assembly to any face having relativelyhigh hardness in order to form a kerf and applying the impactingassembly at other times results in an overall minimization of consumedenergy per ton of fragmented rock and an overall lengthening of the meantime between failure of equipment. The arrangement is well adapted toprogrammed automation of mining cycles. permitting closer supervisorycontrol and reduced manpower requirements.

Other objects of the present invention will in part be obvious and willin part appear hereinafter.

The invention accordingly comprises the processes and devices, togetherwith their steps and elements. which are exemplified in the followingdetailed description. the scope of which will be indicated in the uppended claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of thenature and objects of the present invention. reference is made to thefollowing detailed description. taken in connection with theaccompanying drawings. wherein:

FIG. IA is an exaggerated perspective illustrating a mine faceundergoing a process of the present invention;

FIG. IB is a vertical section. intersecting the mine face. illustratingthe kerf formation step in accordance with the present invention;

FIG. IC is a vertical section. analogous to that of FIG. 1B.illustrating the ripping step in accordance with the present invention;

FIG. 1D is a horizontal section corresponding to that of FIG. 1C.

FIGS. 2A and 2B illustrate certain principles of the present invention;

FIG. 3 is a perspective view of a thermo-mechanical mining apparatusembodying the present invention;

FIG. 4 is a top plan view of an infrared heating subassembly.constituting a component of the device of FIG.

FIG. 5 is a side elevation view of the subassembly of FIG. 4;

FIG. 6 is a detail view of an infrared heating lamp. constituting anelement of the subassembly of FIG. 4;

FIG. 7 is a side view of the infrared heating lamp of FIG. 6; and

FIG. 8 is an electrical schematic diagram part of the control circuit ofthe device of FIG. 3.

FIG. 9 is a cross-sectional view of a mining site typically mined inaccordance with the present invention.

DETAILED DESCRIPTION Rock Formation Toward Which Present Invention isDirected Generally. each of the processes of the present inventiondescribed below involves the rapid excavation of a hard rock mass.ranging in compressive strength from 5.000 to 80.000 p.s.i. (pounds persquare inch). Typi cally, the hard rock mass is one of the commonsedimentary, igneous or metamorphic types. The specific :xamples belowrelate to rock formations from which :opper ore is extracted. In onesuch rock formation to )e mined is a 6 foot thick shale that lies. at adepth 'anging downwardly to 3400 feet. between upper and ower layers ofsandstone. The shale includes intereaved strata of copper rich ore andbarren rock. Varinis mining techniques previously have been employed.Dne technique, called room-and-pillar mining. involves excavating andtransporting ore in such a way as to relain spaced pillars of rock.which continue to support the roof above the floor. Another technique.called longwall mining. involves removing ore without retaining pillarsof rock. while the roof is adequately but temporarily supported by asystem of steel posts or props. which are alternately advanced towardthe receding excavation face in such a way as to permit caving into thealready excavated region. In either case. the ore is loaded into trucksor conveyors for transport.

Thermomechanical Excavation in Accordance with FIGS. IA. 18. 1C. and 1DThe thermo-mechanical apparatus and process of FIG. IA is intended forlongwall excavation of an open ing. particularly a mine opening, havinga floor 32. a roof 34 and an excavation face 35. Typically theexcavation face is several hundred feet wide and approximately five feethigh. In the illustrated embodiment. the heating assembly (FIG. 18)includes a plurality of heating elements 38 enclosed in a plurality ofmounts. one of which is shown at 39. These mounts are disposed alongexcavation face 35, each being individually constrained for reciprocalmotion between an operative position contiguous with the face and aninoperative position remote from the face. The impacting assembly (FIGS.1C and 1D) includes a plurality ofimpacting elements 4| on a singlemount 40 that passes between the face and the heater mounts when thelatter are in their inoperative positions. In the operative mode of theimpacting assembly. a single pass of the impacting mount causesimpacting elements 41 to contact the entire ex cavation face so as torip out an underlying solid increment of rock. i.e., to remove theunderlying rock to a predetermined depth. for transfer by a loader 42 toa conveyor. In this operative mode of the heating assembly. heatingmounts 3') are juxtaposed. either in serial or in parallel. along ahozizontal line 36 between the roof and the floor. in order to causekerf spalling and [one Conditioning. as will be explained in detailbelow. As shown in FIG. 1A. a control 20 transmits synchronizing signalsto mechanical and electrical power units 21. 22 via links 23. 24 andreceives feedback signals from sensors. for example microseismicsensors. which are in contact with the rock. via links 26. 28.

In a first form of the impacting assembly the impacting elements arefixed to their mount so that an eccentric vibratory motion imparted tothe mount is trans mitted to the impacting elements. In one specificexample of this first form of impact or. the assembly weights about22.000 pounds and vibrates 25 times per second over about a 0.2 inch tavel. In a second form ofthe impacting assembly. the impacting elementsare reciprocable along their axes w ith respect to their mount as ittraverses the face linearly. The second form is illus trated asincluding a plurality of tool steel impact moils 4| which arereciprocable. with respect to their mount 40. in a plurality ofcylinders 43. actuated by a power source 45. for example. an electrichydraulic percussion device. As in FIG. 1D, the direction 44 of reciprocation of impact moils 41 is oblique with respect to the excavation faceand the direction 47 of traversal of mount 40 is parallel with respectto the excavation face. In one specific example of this second impactingassembly each moil delivers L000 foot pounds per blow at a frequency ofone to ten blows per second.

Preferably the heating units are combustion free. for example. arecharacterized by an electromagnetic source of infrared or coherentradiation or a charged particle source of electrons or ions. In one suchheating unit. as shown in FIG. 15. heating elements 38 are in the formof infrared emitting lamps which are backed by associated reflectors 45that concentrate the infrared energy at the kerf now to be described.Preferably the temperature at the surface of the kerf ranges betweenl.000 and ].400F and the distance between the heating lamps.specifically the tungsten filaments. and

the excavation face is less than l2 inches. preferably about 4 inches.

In order to facilitate comprehension of the process of the presentinvention. the following definitions are presented.

I. Kerf Space is defined as the empty space of a groove formed by anymeans in a rock face.

2. Kerf Rock is defined as the region of rock immediately adjacent toand so profiling the kerf space.

3. Heat Affected Zone is defined as the region of rock whose resistanceto mechanical ripping has been reduced by heating. which generates solidstate discontinuities at which applied mechanical energy tends toconcentrate. Under this definition. rock in a heat affected zoneexhibits lower resis' tance to mechanical ripping than rock in a zonethat is not heat affected. i.e.. in a zone that has been unaffected byapplied heat or that has not been subjected to applied heat.

4. Thermal Response Class refers to the tendency or lack of tendency ofan in situ rock mass to become heat affected when subjected to heattreatment. It has been found that. in general. the greater thehomogeneity of an in situ rock mass. the greater its tendency to becomeheat affected when subjected to heat treatment. It is useful tocategorize in situ rock mass into the following three classes. it beingunderstood that the boundaries between the classes are only approximate:

a. Class I Rock is defined as the strongest and soundest. mosthomogeneous rock. with major discontinuities or joints on the average atleast two feet apart.

b. Class II Rock is defined as intermediately strong and sound.intermediately homogeneous rock. with occasional specimens as strong asClass I specimens. but with major discontinuities or joints on theaverage less than two feet apart and more than 6 inches apart.

c. Class III Rock is defined as heavily faulted. bedded. and/or jointed.inhomogeneous rock. with discontinuities on the average less than 6inches apart.

. Solid state discontinuities fall into two classes:

a. Natural discontinuities of the type referred to above in connectionwith definition 4. above; and

h. Synthetic discontinuities of the type referred to above in connectionwith definition 3.

In the case of all three classes of rock. it is believed that theefficiency of heat transfer into the mining face is improved byoperation of the impacting assembly which interacts with the heatingassembly by removing fractured rock that would tend to insulate. fromthe heating assembly. the rock underlying the excavation face.

It is further believed that the efficiency of forward penetration of theimpacting assembly into the excavation face is maximized by the heatingassembly in the following manner.

EXAMPLE I In reference to FIG. IB. typically in the case of Class Irock. 4.(l(l() F. tungsten filament electric lamps. 4 inches away fromthe excavation face. heat a l4 inch wide band along the longitudinalcenter of the excavation face for 12 minutes to produce an initial kerfspace 46 that is l to 3 inches deep and a heat affected zone. extendingapproximately to limit 49A in the kerf rock. that is l to 3 inches deep.The heat affected zone then is ripped mechanically to produce a totalkerf space that is 2 to 6 inches deep. It then is feasible mechanicallyto rip the heat nonaffected overkerf rock 48 and underkerf rock 50 toabout the limit 498 to establish again a flat excavation face and torepeat the heating and ripping cycle.

There are interrelated reasons why overkerf and underkerf rock notaffected by heat can be mechanically ripped economically in the presenceof kerf space but not in the absence of kerf space. First. the kerfspace relieves the compressive overburden stresses which hold evenheavily jointed rock together. Second. stresses applied to the overkerfand underkerf rock build up fracturing tensile strenses much morequickly than in the absence of the kerf. After the overkerf andunderkerf rock have been ripped off. it again is not feasibleeconomically to rip the resulting flat Class I rock face onlymechanically. Preferably. during each thermo-mechanical cycle. thethermal spalling at the kerf removes from 3 to 30 percent of the rocktotally separated during this thcrmo-mechanical cycle.

In certain cases. the cracking is aided by chemical agents. which arepresent naturally or may be provided artificially A natural chemicalagent is present in mine rock in the form of considerable amounts offree water. i.e.. water which can be removed at temperatures of aboveZtlllF to 225F. This in situ water is induced by the applied heat todiffuse through the network of cracks formed as above. The effect ofthis moisture transfer may be to reduce the strength of the rock bylowering the specific surface energy of the material. An artificialchemical agent can be applied. for example. in the form of a surfactantsuch as an aqueous detergent sprayed on the excavation face. The effectofthis surfactant is considered. from one viewpoint at least. to reducethe strength of the surface region ofthe rock at and near the miningface.

The additional natural discontinuities in Class II rock and.particularly. in class III rock profoundly affect their characteristicsrelative to those of Class I rock. Specifically. the high concentrationofnatural discontinuities in Classes II and III. in comparison withClass I. cause: l reduced strength of the same order as that caused bythe snythetic discontinuities of the heat affected zone discussed above;(2) reduced speed of sound. a phenomenon which is useful in detectingthe presence ofdiscontinuities (for example. by microseismic sensors);and (3) reduced heat transmissivity. by reason of which thermalspallation may be partially or wholly precluded. One one hand. the abovedescribed heating assembly l spalls Class I rock effectively and (2)spalls Class II rock to a limited extent but (3) does not spall ClassIII roc k. On the other hand. the impacting assembly l may not routinelyrip Class I rock that is unaffected by heat. (2) can rip Class II rockthat is unaffected by heat but preferably is not applied to Class IIrock that is unaffected by heat. and (3) can rip Class III rockroutinely. Thus. the modes ofthe impacting and heating assemblies areinterrelated in such a way as to remove rock from an excavation faceefficiently no matter what its thermal response class.

The production of kerf space 36 and heat affected zone 49A. as in FIG.IB. involves two phenomena: l spallation and (2) thermal cracking.

SPALLATION ANALYSIS Spallation occurs when a conchoidal fragment of rockspontaneously bursts free from the surface of a rock mass that has beensubjected to thermal shock. Spallation also is considered to occur whena fragment loosens but does not burst free of the surface. The prcsentunderstanding of the mechanism of spallation is as follows:

FIG. 2A shows an intense heat flux (BTU/hr/ft") 51 impinging on a rocksurface 53. As the surface is sub jected to thermal shock. a thermalgradient 55 along an axis 57 is developed in the rock mass. The shape ofthe gradient. depth .r versus temperature I is a function of heat fluxintensity. i.e.. rate of heat transfer. The induced thermal stress is adirect function of the thermal gradient. The stress most important tospallation is the tensile stress 0', parallel to the axis and thecompres sive stress tr, perpendicular to the X axis. These stresses areillustrated at 59 and 61. Rock. being a brittle material. tends to breakin tension. Therefore. if a discontinuity ofcritical size andorientation exists in the region of maximum 0,. as shown in FIG. 2A. acrack will initiate as at 63 and will propagate in the directionindicated by the arrows. In a real situation. the crack propagation pathwill depend on the shape of the heat flux distribution and on thecompressive stress state (I... The tensile stresses initiate fracturebut the stored strain. due primarily to compressive stress 0... providesthe kinetic energy to extend the crack and to cause the fragment tospall. It is believed that. in Class I and more often in Class II rock.even a negligible compressive stress 0,. often propagates a tensilecrack with the result that a flat plate-shaped fragment loosens from therock mass but lacks the strain energy to burst free.

THERMAL CRACKING ANALYSIS In connection with thermal cracking. a thinlayer of rock. I to 5 inches deep. which is to become or has become kerfrock. is heated to a temperature ranging upwardly to approximately 500F.

Stresses developed by the thermal gradient are upproximated by:

0' EaA T/l-v Where:

0' confined thermal stress E modulus of elasticity u Poissons ratio AT tI0) I, final temperature T initial temperature It can be shown thatstresses can be developed within the rock mass. of the magnitude of therocks tensile strength, by a temperature increase of 70F above i with EX a 5 X [0. v= 0.3. and 1 80F. Laboratory tests have shown that thetensile strength as a function of temperature, for so-called Red MassiveRock, is a minimum of 1000 pounds per square inch in the range of 200400F. Below 200F to room temperature the strength continually increases.These data indicate that cracks can be initiated at very low temperaturegradients and that a crack. once started. propagates with ease. eventhrough cold rock is permitted by boundary displacements. Such cracksare suggested at 67 in FIG. 2B.

As indicated previously, in situ rock often naturally contains from a to2 gallons of free water. It is believed that this water is forced intomotion by pressure due to any thermal gradient. by vacuum generated atany crack apex. and by wetting (spreading) ofdry rock surfaces. eg a newcrack surface. The water then reacts with the rock surface to reduce itsspecific surface en ergy The strength of brittle materials is given as:0'

V-iEy/rrC Where:

0' applied stress E modulus of elasticity y specific surface energy Cinherent crack length The above relationship indicates that as y isreduced. rock strength is reduced. and that as crack length increases.rock strength is reduced. Further weakening occurs as a result of steamformation and condensation EXAMPLE ll Thermal Alone 228.000 BTU/ton X200 ton/hr X 1/047 97 X 10 BTU/hr (for 200 tons/hr) ThermomechanicalThermal Energy 50 tons/hr X 228.000/0.47 BTU/ton 24.3 X l0 BTU/hr (for50 tons) Mechanical Energy 300 hp 2544 BTU/hr 0.764 X l0 BTU/hr (for 150tons) Total 25.06 X 10 BTU/hr. (for 200 tons) Ratio /97 =0.258 25.8percent EXAMPLE lll It was found that spallation rates. in grams perminate, at a depth of 1.l [0 feet underground and at a depth of feetunderground, were in the ratio of approximately 375 to one. Thisobservation illustrates that the final stress state is a superpositionof various stresses which are induced by tectonic forces. excavation configuration, heat distribution etc. Thus, stresses in rock due to naturalcauses can be used advantageously, in combination with stresses due toartificially applied energy, for fragmenting rock. Specifically. thedeeper the excavation the greater the natural stress state and thegreater the spallation effect for a given amount of applied heat flux.

The Thermo-mechanical Longwall Mining System of FIG. 3

ln longwall copper ore mining. typically. two parallel service tunnelsare driven from 200 to 800 feet apart and are connected by a thirdtunnel or gallery. Ore then is separated from the retreating wall(mining face) of this gallery while the roof of this gallery issupported above steel caps that are carried by props. These props andcaps are designed to support the weight of the overlying rock, with anample factor of safety. As each incremental depth of slice of ore ismined. the props together with the caps. in a sequence of steps. arereleased, moved forward toward the mining face and reinstalled. In thenewly unsupported regions remote from the mining face caving occurs intothe underlying excavated region.

FIG. 3 illustrates a longwall face 50 of a gallery 52 that extendsacross and beyond a pair of service tunnels at 54 and 56. A plurality ofprops 58 extend from the mine floor 60 upwardly to a plurality of caps62, on which the roof of the gallery is supported. Adjacent to thelongwall face is a series ofinfrared heaters 64, each of which isconstrained for reciprocal motion at right angles to the longwall faceby a drive linkage 66 and a pair of parallel rails 67. Adjacent to thelongwall face also is a mechanical ripping and plowing unit 68, which ismovable along the longwall face under the control of a chain 69 onsuitable wear and back plates that are parallel to and adjacent to thelongwall face. Mechanical ripping and plowing unit 68 includes a plow 71(details not shown) and two series impact moils 73a. 73b at oppositevertical edges of the plow. When unit 68 is moving in one direction.impactors 730 are oriented obliquely in mechanical contact with thelongwall and when unit 68 is moving in the other direction. impactors7311 are oriented obliquely in mechanical contact with the longwall. thearrangement being such that ripping of the longwall occurs with eachpass of unit 68 in either direction. Plow 71 includes an upwardly andoutwardly directed inner face by which rock is scooped from the vicinityof the longwall and channeled onto a panzer conveyor 75. Unit 68 andconveyor 75 are con trolled by drive motor 77 and gearing 79, 81. Thearrangement is such that heaters 64 focus infrared radia tion along azone between the floor and the roof. se quentially producing a region ofweakness having greater than the original discontinuity density. As unit68 is moved along the longwall. each of heaters 64 in sequence isretracted to permit unit 68 to pass between it and the longwall face andis returned to proximity with the longwall face after unit 68 hascleared. This reciprocal movement of each heater is under the control ofthe position of unit 68, which automatically initiates dimming in orderto maximize equipment life and to economize electrical powerconsumption. The

heater. ripper and plow device and the conveyor are advanced as a unittoward the longwall face, as the mining process continues, by the actionof hydraulic cylinders anchored at one end to the roof support props andat the other end to the panzer conveyor. Props 58 which normally arepressured between the floor and the roof of the mine. are advanced by: Isequentially releasing the caps 62 on one set of props. (2) retractingthe horizontal cylinder attached between the props and the panzerconveyor, and (3) repressurizing the freed caps 62 against the roof in anew advanced position. The process is repeated for adjacent props. downthe length of the longwall until all have been repressurized at advancedpositions.

The Infrared Heating Unit of FIGS. 4, 5 and 6 As shown in FIGS. 4, 5 and6, each heating unit comprises a housing 80 within which the operatingcomponents are mounted and enclosed. Within the housing, infraredradiation is generated by a bank 82 of six groups of six electricallyenergized lamps. which are arranged to present a perpendicular faceemitting infrared radiation. Behind each lamp is positioned a reflector84. by which infrared radiation from the lamps is focused on the miningface for the purpose of producing a zone of discontinuities. Mounted atthe front face of housing 80 in order to protect the lamps fromfragmented rock are a coarse outer screen 88 and optionally a fine innerscreen 90. Between the screens and the lamps is a quartz plate 91 whichshields the lamps drom dust while passing infrared radiation. A blower92 blows cooling air through the housing. via a filter 94 at the rear,past the lamps and through openings at the front.

Details of one of the lamps are shown at 96 in FIGS. 6 and 7. which isone example of a suitable lamp. This lamp includes a U-shaped quartzenvelope having a bight 98 and a pair of legs I00, I02. Within bight 98is a tungsten filament 104, the opposed ends of which are integral withtungsten leads 106, 108 to metal terminals I10, I12 (FIG. 6.). Thus theglass to metal seals at the free extremities of legs I00. 102 are spacedfrom the heat emitting bight in order to reduce seal temperature and toincrease lamp life. Also the glass to metal seals, when the lamp is inoperation. are located behind reflectors 84 so as to be air cooledefficiently. In one case lamp has a inch radiating length of filamentconsum ing 2.000 watts of electricity at a tungsten filament temperatureof 4000F and 86 percent of the total elec trical input or I720 watts ofinfrared radiation is emitted from the lamp in the wavelength range of0.6 microns (yellow) to 4 microns (infrared). Non radiating spacebetween the lamps is about W2 inches.

The function of reflectors 84 is to collect and redirect onto theminewall face as great as possible a fraction of the backwardly directedenergy. Preferably the reflector is composed of material. having a highcoefficient of reflectivity for the band of wavelengths emitted by theinfrared lamps and yet being mechanically strong and capable ofoperation at elevated skin temperatures with minimum cooling. The energythat is absorbed by the reflector causes a surface layer several micronsthick to become hot and to re-radiate. Examples of materials which aresuitable for reflector construction are magnesium oxide, magnesiumcarbonate and aluminum oxide. These compounds can be molded and firedinto hard briquettes having high reflecting pure white surfaces. Theyare self-cleaning and can operate at high surface temperature withoutdamage.

In one case, blower 92 has a capacity of 400 to L000 c.f.m. to providecooling air for the lamp leads. the quartz lamp body and the reflectorsurfaces. A large portion of the air is directed to pass between thelamps and the reflectors so as to lower the surface temperature ofquartz lamps to about l,600F. In addition, the thermal energy absorbedby the outgoing air is directed through the front of the lamp enclosuretoward the minewall. whereby additional preheating of the wall iseffected.

Operation of the Thermo-mechanical Longwall System of FIG. 3 inReference to FIG. 8

Each of heaters 64 of the device of FIG. 3 contains a control circuit ofthe type shown in FIG. 8. This circuit, which incorporates six lamps. isenergized by a transformer 120. A master switch I22. when closed.applies the output of the secondary of transformer I20 across sixparallel paths each of which includes a power relay 124 (for anassociated lamp). a current relay 126 and a power level toggle switch128. The arrangement is such to establish across the lamps, a normalcurrent which is the maximum current maintained across the lamps whenthe device of FIG. 3 is in operation with all switches 122. 126. 128closed. When any heater 64 is retracted to its position remote from theexcavation face, its associated switch 128 opens to economize powerconsumption while preventing undue lamp cooling, which might give riseto thermal shock. When any heater 64 is extended to its positionadjacent to the excavation face, switch 122 closes.

Optional Separation of Ore and Gangue at the Mining Face In Reference ToFIG. 9

FIG. 9 is a cross-sectional view of a geological formation in which thesystem of the present invention typically is employed. Thiscross-section specifically de picts a geological formation in the coppermine of the White Pine Copper Company. White Pine. Michigan. The broaddesignation of parting shale and upper shale ore strata actually arecomposed of alternating substrata of rich and lean copper bearingmaterial as shown at 132 for copper-rich and at 134 for copper leanstrata. In one form. impactor 40 of FIG. 1C is designed so that on onepass it gouges out lean strata 134, separating and discarding thefragments of such strata from the rich strata 132. which latter is theonly material that is further processed through the crushing. grinding.milling and flotation circuits. Ripping of the entire parting shale isknown as values-only mining because. in contrast to room-and-pillar"mining. essentially none of the barren upper and lower sandstone ismined with the copper bearing shale. The foregoing technique of optionalseparation of ore and gangue at the mining face might be called trulyvalues only since it not only avoids dilution of the shale ore withbarren sandstone. but it also minimizes further processing of barrenstrata of the parting shale itself. FIG. 9 also illustrates longwallmining and caving with the use of movable posts I36.

CONCLUSION The above described embodiment of the present inventioninvolves the synergistic combination of thermal energy and mechanicalenergy for efficiently fragmenting hard rock from a mining or tunnelingface. In its broadest sense. the heating assembly is the preferred oneof many types of thermal. hydraulic. abrasive and laser units that canact to cut kerfs in an excavation face. Since certain changes may bemade in the above disclosure without departing from the scope of thepresent invention. it is intended that all matter contained in theforegoing description and shown in the accompanying drawing beinterpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. An excavation apparatus for continuously excavating rock fromsuccessively exposed excavation faces. said excavation apparatuscomprising a heating means constrained for movement between an operativemode and an inoperative mode. an impacting means constrained formovement between an operative mode and an inoperative mode. said heatingmeans when in its operative mode being contiguous with one of saidsuccessively exposed excavation faces in order to apply thermal energyto selected portions thereof. said heating means when in its inoperativemode being remote from said one of said successively exposed excavationfaces. said impacting means when in its operative mode passing betweensaid one of said excavation faces and said heating means in order toapply mechanical energy to all portions thereof. means for sensing andindicating the homogeneity of said rock underlying said one of saidsuccessively exposed excavation faces. and control means for selectingthe mode of said heating means and the mode of said impacting means inresponse to deter minations of said means for sensing and indicating.

2. The excavation apparatus of claim 1 wherein said heating meansincludes a plurality of infrared elements.

3. The excavation apparatus of claim 1 wherein said impacting meansincludes a plurality of impacting elements.

4. The excavation apparatus of claim 3 wherein impacting elements arecarried by a single mount.

5. The excavation apparatus of claim I wherein said heating meansincludes a bank of infrared emitting tubes. reflectors rearwardly of andrespectively associated with said tubes for focusing radiation therefromtoward said excavation face. an infrared transparent sheet forwardly ofsaid bank. and screen means forwardly of said infrared transparent sheetfor protection against rock fragmented from said excavation face.

6. The excavation apparatus of claim 1 wherein said heating meansincludes a plurality of infrared generat' ing elements disposed along aline approximately midway between the floor and the roof bounding saidone of said excavation faces is i said

1. An excavation apparatus for continuously excavating rock fromsuccessively exposed excavation faces, said excavation apparatuscomprising a heating means constrained for movement between an operativemode and an inoperative mode, an impacting means constrained formovement between an operative mode and an inoperative mode, said heatingmeans when in its operative mode being contiguous with one of saidsuccessively exposed excavation faces in order to apply thermal energyto selected portions thereof, said heating means when in its inoperativemode being remote from said one of said successively exposed excavationfaces, said impacting means when in its operative mode passing betweensaid one of said excavation faces and said heating means in order toapply mechanical energy to all portions thereof, means for sensing andindicating the homogeneity of said rock underlying said one of saidsuccessively exposed excavation faces, and control means for selectingthe mode of said heating means and the mode of said impacting means inresponse to determinations of said means for sensing and indicating. 2.The excavation apparatus of claim 1 wherein said heating means includesa plurality of infrared elements.
 3. The excavation apparatus of claim 1wherein said impacting means includes a plurality of impacting elements.4. The excavation apparatus of claim 3 wherein said impacting elementsare carried by a single mount.
 5. The excavation apparatus of claim 1wherein said heating means includes a bank of infrared emitting tubes,reflectors rearwardly of and respectively associated with said tubes forfocusing radiation therefrom toward said excavation face, an infraredtransparent sheet forwardly of said bank, and screen means forwardly ofsaid infrared transparent sheet for protection against rock fragmentedfrom said excavation face.
 6. The excavation apparatus of claim 1wherein said heating means includes a plurality of infrared generatingelements disposed along a line approximately midway between the floorand the roof bounding said one of said excavation faces.